Of course countries can do whatever they want (just from the notion of application of power). But I see immigration as a two way street. There's an invitation to come into a society, and a request to participate in it. Other people in society get second chances, they get opportunities to improve... I feel like extending that to everyone is the logical conclusion of a just society.
And... yeah maybe there's some abstract notions that underpin the US system. But when you look at the facts on the ground, I just don't see how you justify the draconian decisions applied to people after they've been a part of society for so long. What's the point of a bunch of theory if the practice turns into things like "ICE can lock someone up for years without them being allowed to see a judge"?
At least it's not at Australia-level cruelty, I guess...
Even beyond than that, there are multiple facets of both legal and illegal immigration. Maybe the US both accepts larger numbers of immigrants legally but is also more intolerant of certain kinds of applicants than others.
When dealing with huge issues, I think it's deceptively easy to simplify the issue more than you realize. I know I've ended up in arguments where after far too much effort I realized we both actually more or less agreed with each other, but were simply focusing on different aspects of a larger issue.
"most countries _don't_ just kick someone out on the first crime they commit."
Neither does the US. Most of the time the crimes that lead to deportation are felonies. Why is the US obligated to keep non citizens who commit serious crimes?
The US is under no obligation to take anyone.
The system certainly isn't perfect, warrants criticize. But some of the complaints are ridiculous and come down to again way more demand than supply.
(Update, I don't agree with you, but I hope HNers will not downvote you as a few are)